The development of new blood vessels (angiogenesis) is fundamental not only during embryogenesis but also as a protective response in adult tissue subjected to ischemia. To be productive, the formation of endothelial lined vessels is typically followed by the recruitment of perivascular cells. This maturation process produces functional vessels which persist over time and are responsive to physiological stimuli. The production of mature vessels is of therapeutic importance in the treatment of ischemic disease. However, there has been little success in stimulating the formation of mature microvessels in adults.
Angiogenesis is a physiological process involving the growth of new blood vessels from pre-existing vessels. Angiogenesis entails the proliferation and migration of endothelial cells to form immature vascular networks. There is also a maturation phase of angiogenesis that entails the recruitment of mesenchymal cells, including pericytes and/or smooth muscle cells (SMCs), which wrap the newly formed vessels to stabilize them. This is referred to as angiogenic maturation. Such angiogenic maturation may be the process of a recent angiogenic event, or include maturation, maintenance, and stabilization of vessels generated through angiogenesis at any point in development and post-natally. Angiogenic maturation may also include the process of maturation, supporting, and stabilizing of blood vessels generated through the process of vasculogenesis as defined by the de novo condensation of appropriate stem, progenitor, or more differentiated cell types into tubular vessels.
A number of proteins, typically referred to as angiogenic proteins, are known to promote angiogenesis. Such angiogenic proteins include members of the fibroblast growth factor (FGF) family, the vascular endothelial growth factor (VEGF) family, the platelet-derived growth factor (PDGF) family, or the insulin-like growth factor (IGF) family. For example, certain FGF and VEGF family members have been recognized as regulators of angiogenesis during growth and development. Their role in promoting angiogenesis in adult animals has also been examined.
Angiogenic proteins, such as FGF family members, have been disclosed in many patent documents, for example U.S. Pat. No. 4,956,455 (titled Bovine fibroblast growth factor, issued Sep. 11, 1990), U.S. Pat. No. 5,155,214 (titled Basic fibroblast growth factor, issued Oct. 13, 1992), U.S. Pat. No. 5,302,702 (titled Chimeric fibroblast growth factors, issued Apr. 12, 1994), U.S. Pat. No. 5,314,872 (titled: Glucan sulfate, stabilized fibroblast growth factor composition, issued May 24, 1994), U.S. Pat. No. 5,352,589 (titled Deletion mutant of basic fibroblast growth factor and production thereof, issued Oct. 4, 1994), U.S. Pat. No. 5,371,206 (titled DNA encoding chimeric fibroblast growth factors, issued Dec. 6, 1994), U.S. Pat. No. 5,387,673 (titled Active fragments of fibroblast growth factor, issued Feb. 7, 1995), U.S. Pat. No. 5,439,818 (titled DNA encoding human recombinant basic fibroblast growth factor, issued Aug. 8, 1995), U.S. Pat. No. 5,491,220 (titled Surface loop structural analogues of fibroblast growth factors, issued Feb. 13, 1996), U.S. Pat. No. 5,514,566 (titled Methods of producing recombinant fibroblast growth factors, issued May 7, 1996), U.S. Pat. No. 5,604,293 (titled Recombinant human basic fibroblast growth factor, issued Feb. 18, 1997).
The fibroblast growth factors (FGF) are a family of at least twenty-three structurally related polypeptides (named FGF1 to FGF23) that are characterized by a high degree of affinity for proteoglycans, such as heparin. The various FGF molecules range in size from 15-23 kD, and exhibit a broad range of biological activities in normal and malignant conditions. Activities that have been characterized for FGF molecules include nerve cell adhesion and differentiation; wound healing; as mitogens toward many mesodermal and ectodermal cell types, as trophic factors, as differentiation inducing or inhibiting factors; and as an angiogenic factor. For example, PCT Publication WO98/50079 (titled Techniques And Compositions For Treating Heart Failure And Ventricular Remodeling By in Vivo Delivery Of Angiogenic Transgenes, published Dec. 30, 2004) describes the use of FGF2, FGF4, or FGF5 to ameliorate regional myocardial contractile dysfunction in an animal model of heart failure. The therapeutic mechanism of action is stated to be angiogenesis.
Angiogenesis entails the proliferation and migration of endothelial cells from the existing vasculature in order to create new blood vessels. These nascent vessels are incomplete as they lack supporting layers of mature smooth muscle cells (SMCs). As a result, immature vascular beds are prone to regression due to the fact that endothelial cells retract and eventually undergo apoptosis. Stabilization of newly or previously formed blood vessels through angiogenic maturation by SMCs both prevents regression while also conferring the critical ability to regulate blood pressure. While a number of factors that stimulate the recruitment of SMCs to blood vessels during development have been identified, these pathways are poorly understood with respect to postnatal angiogensis.
Currently, blood vessel formation stimulated by established soluble angiogenic cytokines either in vivo or simulated in vitro are short-lived due to the fact that they lack complete layers of supporting SMCs and are therefore of limited therapeutic or experimental value.